good info on all! thanks. Will get a bigger pot and do a sweep and
see if I can find a value, just helps me get a clue into whats going on, I like
to play.
the amp is excellent on 80 and 40 now, so I am playing with these values to
figure out
where 20 and if I can, get 15 to work.
big flea market coming up in a few weeks in Hopkinton NH so will be scrounging
and selling
stuff there!!!
-----Original Message-----
From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com]On
Behalf Of Peter Voelpel
Sent: Tuesday, April 18, 2006 6:43 PM
To: amps@contesting.com
Subject: Re: [Amps] working backwards to setup tank
Hi Chuck,
if I remember right you are running 3.9KV at the anode, 3.5KV under load.
With 500W output you have most likely not more then 250mA anode current.
That results into an impedance of almost 8000 ohms.
It is a good chance that you tuned to a harmonic with such a small pi coil
calculated at 2100 ohms which can´t be right either, since you talked about
expected 2A to be drawn, which results into half of it, about 1000 ohms.
With 1 A you are about right with 2100 ohms.
Then on 7.25MHz you should have a total plate capacitance of about 115pf, a
coil of 4,97µH and your loading capacitor at 600pf, all calculating for full
load, 1A and about 2275W output and a Q of 12 at 2100 ohms.
At 8000 ohms for 500W you can´t hold Q=12 because your minimum capacitor for
the anode capacitor is already too high, you have to raise it to 15 or even
higher if your capacitor is very large.
Values for 8000 ohms are:
anode-C incl. strays 37pf, coil 14.4µH and load-C 195pf, Q=15
73
Peter
-----Original Message-----
From: amps-bounces@contesting.com [ <mailto:amps-bounces@contesting.com>
mailto:amps-bounces@contesting.com] On Behalf Of Partain, Chuck
Sent: Dienstag, 18. April 2006 23:21
To: amps@contesting.com
Subject: [Amps] working backwards to setup tank
in ref to my gu-84b based hf amp
I set this tank circuit up and tuned at 7.250mhz, came up with a beautiful
output then tried to do the reverse check. I put a 2k resistor from the
plate to ground, hooked the MFJ analizer up using the settings previously
obtained and for th e life of me cannot find a good resistive value to make
the swr analizer 1:1 swr or close. I used a 15k pot and even went SLOWLY one
end to the other and best I see is 3 to one!!! what am I doing wrong?? I
used a 2k load to get CLOSE to where I want to set the plate and load caps
and the inductance was setup using a formula with 2100 ohms plate reactance.
Once running, I went to 500 watts and am using those settings.
sorry if I am not clear but maybe someone understands my drivel :)
ka1mwp
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